Rudy Hermann Guede, 20, from the Ivory Coast, told a court in Germany that he was innocent of Miss Kercher's murder, but did not deny that he had been at the scene of the crime.

Miss Kercher, 21, from Coulsdon, south London, was found in her bedroom in Perugia on Friday November 2 with her throat cut. Police believe she was forced into an "extreme" sexual game before being killed.

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However, the circumstances of Miss Kercher's death were muddied further when Guede allegedly told a friend that Amanda Knox, 20, had not been at the house when Miss Kercher died.

Instead, he said that a "brown-haired Italian" had been the assassin.

Guede is reported by La Nazione, a newspaper, to have made the allegation while chatting on the internet to a friend, with the police listening in. He is reported to have told his friend that Miss Kercher had invited him to her room, to make love.

He then claimed he went to the bathroom, and in the meantime, someone rang the doorbell.

After that, he heard Miss Kercher's screams. "I had a fight [with the man], and I was wounded. I do not remember his face precisely, but then I ran away scared. I did not kill her."

Other witnesses have told the police that they were bumped into by a "man of colour" running away from the scene at roughly the same time.

Knox, and Raffaele Sollecito, 23, her boyfriend, are both in custody on suspicion on murder and sexual assault. The prime piece of evidence against them is an eight-inch kitchen knife, found at Sollecito's house.

The knife allegedly has traces of Knox's DNA near the handle and of Miss Kercher's DNA at the tip.

While police attention was focussed on Patrick Diya Lumumba, the 37-year-old Congolese bar owner who has since been released from custody, Guede was able to make a get-away to Germany, where he was sleeping rough on a barge on the river Rhine.

However, in a rambling hand-written letter, Knox said she had been put under such pressure to confess by the police that her testimony was worthless.

Knox wrote the letter at 11pm on the day of her arrest, asking for sheets of blank paper and a pen while in custody.

"I have serious doubts about the truth of my statements," she wrote, "because they were made under stress and shock and I was exhausted. I am very confused. At this point, my head is full of ideas and I am unable to control them."

She added: "I was told I would be arrested and put in prison for 30 years.

When I could not remember, things jumped out of my head. After all these hours of confusion, these responses came out."

She said she had not asked her boyfriend, Sollecito, to provide her with an alibi, and instead said that at one point, she recalls him with "blood on his hands".

However, she said she thought it was blood from a fish they had cooked for dinner.

She said Sollecito was now trying to "distance" himself from her.

His father has said Knox "ruined" Sollecito's life.

Knox, in turn, has alleged to police that Sollecito was a user of "cocaine and acid in the past, even if he now says he only smokes weed" and that "he is often depressed and sad".

One of Knox's friends, Spyros Gatsios, told police that Knox liked Sollecito because "he was very timid".